Composite image of the Milky Way, the spiral galaxy in which our solar system lies. Our Sun is believed to be around two-thirds of the way out from the centre in a small spiral arm. The Galactic Centre is at the centre of the image in the constellation Sagittarius. This is where the bulge of stars in the Milky Way is at its greatest, tapering away on either side. The image runs around the whole of the sky, so our view away from the Galactic Centre is seen both at far left and at far right. Interstellar dust obscures much of the Galaxy's central axis. The Milky Way is thought to be about 120,000 light years across and to contain over 100 billion stars.